DC motors having brushes and commutators have been long known in art, but are still capable of significant improvement. Commutation in a conventional DC motor occurs when a brush provides a short circuit between two ends of an individual motor coil. Prior to commutation, current is flowing through coils lying on one side of the brush in one direction, and current is flowing through coils lying on an opposite side of the brush in the reverse direction. After commutation, current flows in an opposite direction through the commutated coil. To ensure good commutation, current density in the brush at the beginning and the end of commutation should be low, and the voltage difference between the brush and the commutator segment should also be low. However, even with linearly decreasing current during commutation, the energy associated with the residual current must be dissipated before the current can reverse. The commutator and brushes act as a heat sink to absorb this energy, and this provides the high temperature that shortens the life of the brushes. Typical commutation can produce sparks or flashovers, where large currents are rapidly discharged between partially contacting contact surfaces.
Nevertheless, commutation in brush-type DC motors has cost and design advantages when compared to the electronic commutation utilized by brushless motors. For consumer products, such as electric vehicle motors, a long brush life expectancy will attract consumers to choose a low-cost brush-type motor that does not require a costly inverter.